We’ve widely acknowledged that the anti-Xa assay, currently employed to monitor heparin therapy, may be readily adapted to measuring direct oral anti-Xa antthrombotics, and at least three hemostasis diagnostics manufacturers have developed and validated rivaroxaban and apixaban calibrators and controls for this purpose. These await US FDA clearance. Meanwhile, we estimate oral anti-Xa antithrombotic efficacy with the prothrombin time. A colleague has asked, what does the lab offer when a surgeon chooses to transition a patient from rivaroxaban to heparin in preparation for major surgery, an everyday occurrence? Since the PT doesn’t measure heparin and the PTT doesn’t respond to rivaroxaban, it seems the simplest way to document rivaroxaban clearance before starting heparin is to employ the anti-Xa assay on a RUO basis. Do any of our participants have an alternative recommendation?